PLAN’ PHYSIOLOGY 125 
ment is carefully done, it is possible to see some result 
at the end of a month, while in two months the differ- 
ences in the plants are quite striking. If the solutions 
in the bottles get too low, they should be filled up with 
distilled water. 
Results.—At the end of eight or ten weeks, the only 
plant that has grown well is the one in the Normal Solu- 
tion; the one without iron has grown tall, but all the 
new leaves are white; the one in distilled water has 
hardly grown at all, nor has the one without nitrogen. 
Deductions.—Iron is necessary for the formation of 
green colour, and all the other elements are necessary for 
healthy growth. | 
88. Absorption.—Much of what we know about the 
absorption of water by roots and its passage through the 
plant was discovered by Stephen Hales in 1727, but he 
knew very little about the chemical substances present 
in the soil which are absorbed with this water. Water 
occurs in the soil under two conditions, (1) free water, 
which trickles through the soil if it is properly drained. 
(2) Capillary water, which adheres to the surface of 
soil grains, and to plant roots in thin films. It is this 
capillary water which is absorbed by the roots, and it 
contains various dissolved substances, such as sodium 
chloride, calcium carbonate, etc. The Root-Hatrs are 
the organs which absorb this water. They come into 
close contact with the particles of soil, so that when a 
seedling is pulled up we always see soil adhering to it 
wherever the root-hairs occur. The process by which 
root-hairs are enabled to absorb water is Osmosis. 
Whenever two liquids of different densities are separated 
